On Tue 06-09-11 18:18:56, Peter Zijlstra wrote: > On Sun, 2011-09-04 at 09:53 +0800, Wu Fengguang wrote: > > De-account the accumulative dirty counters on page redirty. > > > > Page redirties (very common in ext4) will introduce mismatch between > > counters (a) and (b) > > > > a) NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied > > b) NR_WRITTEN, BDI_WRITTEN > > > > This will introduce systematic errors in balanced_rate and result in > > dirty page position errors (ie. the dirty pages are no longer balanced > > around the global/bdi setpoints). > > > > So wtf is ext4 doing? Shouldn't a page stay dirty until its written out? > > That is, should we really frob around this behaviour or fix ext4 because > its on crack? Fengguang, could you please verify your findings with recent kernel? I believe ext4 got fixed in this regard some time ago already (and yes, old delalloc writeback code in ext4 was terrible). Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>